class_docstr: *MUSAN* :cite:`musan2015` dataset.
  
  Args:
      root (str or Path): Root directory where the dataset's top-level directory exists.
      subset (str): Subset of the dataset to use. Options: [``"music"``, ``"noise"``, ``"speech"``].
code: def __len__(self) -> int:
      return len(self._walker)
  
file_path: audio/src/torchaudio/prototype/datasets/musan.py
imports: from pathlib import Path
  from typing import Tuple, Union
  import torch
  from torch.utils.data import Dataset
  from torchaudio.datasets.utils import _load_waveform
label_desc: Use image node_id 4 for calling the Musan obj's underlying member method code with example usage: obj.__len__() and returns: len